The invention relates to a system which will detect and measure the harmonic content of 60 Hz current.
A problem which is increasing in importance is the amount of harmonic current generated in branch circuits. Such harmonic current is produced by most electronic power supplies. With the ever increasing number of personal computers, work stations, printers, etc. connected to a user facility's power circuit, the level of harmonic current can overload branch circuit wiring. Also, excessive harmonic current is detrimental to efficient utility power transmission and distribution.
To more precisely describe the problem caused by harmonic current, power supplies for use in computers and other electronic equipment sometimes utilize power line current in a non-sinusoidal form. The result is that harmonic currents are taken from the power line. This phenomenon can be particularly bothersome with regard to the current in the neutral line of a 3 phase circuit. In such a circuit, the harmonics do not cancel each other out as do fundamental sine currents. The neutral line, if not designed to compensate for this harmonic current, may overheat. Also, the utility supplying the user may find that its station and substation equipment, as well as its neutral wire, (transmission and/or distribution) is undersized in view of the harmonic current.
This phenomenon is widespread because most buildings were designed before the proliferation of electronic equipment with power supplies such as hereinbefore described, and consequently they are vulnerable to circuit failure within the building.
To more fully describe the problem presented by currents and harmonic frequencies, and assuming a fundamental frequency of 60 Hz, the harmonics would be 120, 180, 240, 300, etc. Hz. In general, the problem is caused mainly by the "harmonics that are multiples of 3," i.e., 180, 360, 540, 720, etc. Hz. These harmonics do not cancel in the neutral conductor. Thus, if the wiring was originally "sized" for pure sine waves, as was the case before the proliferation of electric power supplies, the neutral conductor may be undersized for modern loads, such as p.c.s, terminals, workstations, printers, etc. Additionally, as previously implied, the utility generating and distributing equipment can be overheated by the harmonic content of the load currents.
A similar problem exists with regard to the utility in that it would like to be able to measure and detect harmonic current and thus produce or buy equipment to take care of the problem. The benefit to the utility would lie in its ability to charge customers for remedying the problems caused by this harmonic current.